Application of Dislocation Theory to Internal Friction Phenomena at High Frequencies

Abstract

A detailed discussion of data obtained over the past 15 years concerning the damping of mechanical vibrations in the kilocycle and megacycle range is given. The dependence of the decrement and modulus change on the variables of frequency and strain-amplitude and many other parameters is compared with predictions of the dislocation theory developed in an earlier paper. Although general agreement is obtained, and many interesting quantitative results are found, it is not possible to say that the theory agrees everywhere since not all the necessary parameters are known well enough theoretically. A number of new experiments are suggested which may permit stronger conclusions to be made. This part may be read independently of the earlier paper by the reader who does not wish to follow the development of the theory in detail.

Effects of Heat Treatment on the Morphology of Long-Period Stacking Ordered Phase and the Corresponding Damping Capacities of Mg-Cu-Mn-Zn-Y Alloys

“…2(c) also reveals that 14H unit cells are obtained to make up the 14H structure. Upon treatment of the solute at 813 K, some studies show that the RE and Zn atoms in the Mg 24 (RE,Zn) 5 and (Mg,Zn) 3 RE phases diffuse into the matrix whereas the Mg 12 ZnRE phase remains as a gray block phase because that the LPSO phase is relatively stable at high temperatures. 12,13) As can be seen from the Fig.…”

“…4,5) At low strain amplitude, the movable dislocations are nailed by strong pinning, that they only move between weak pinning as reciprocating motion, thereby generating low internal friction in the alloys. After heat treatment of the alloys, the mass of solute atoms dissolve into the ¡-Mg matrix increase the number of weak pinning points.…”

“…19) At the same time, according to the Granato-Lücke dislocation damping theory, 4,5) the damping caused by dislocation movement in the low temperature range is direct proportional to the dislocation density and is related to the strain amplitude and vibration frequency. As test parameters which mean strain amplitude, Alloy III P 1 peak P 2 peak P 3 peak loading frequency, temperature range and heating rate are same, peak P 1 of the alloy I and alloy II are almost annihilated.…”

“…However, it is believed that the behaviors of pure magnesium and some magnesium alloys conform with the GL theory. 4,5) In this case, the damping capacity of magnesium alloys is closely related to the interaction between the movement of dislocations and point defect, including solute atoms, secondary phases, and point vacancy. Meanwhile, strengthening materials traditionally involves controlled creation of internal defects and boundaries to obstruct dislocation motion.…”

Acoustic Harmonic Generation and Dislocation Dynamics of Fatigued Aluminum Alloys

“…Another source is associated with the nonlinearity in the displacement (bowing) of a single dislocation between pinning points under an applied stress. The latter source of hannonic generation was predicted by Suzuki et al[l] by including nonlinear terms in the Granato-Lucke theory [4,5] of the interaction of an acoustic wave with pinned dislocations described by the Koehler string model [6]. The model of Suzuki et al[l] predicts the second hannonic to be linearly dependent on the applied or residual stress in the solid and dependent on the dislocation loop length to the fourth power.…”